I also noticed a slow using Geonear with 2dsphere index,
but what is slow, im pretty new with mongo so imnot sure ,
here is the context:
i make a full scan over 35000 item collections with no limit result,
it takes about 5s on a 1core vm google cloud machine.
If its not a normal things (i guess) , i can provide you the collection for reproduce pb;
We just discover mongo and love it but this limitation is a serious blocker for us project.

db.runCommand({ geoNear: "tablegui", near: [2.298800, 48.854355], spherical: true, distanceMultiplier: 6371 , maxDistance:2000/6371 , limit:37000 });

"stats" :
{ "nscanned" : NumberLong(810310), "objectsLoaded" : NumberLong(810310), "avgDistance" : 325.45877488880984, "maxDistance" : 701.9530252234592, "time" : 5511 } , "ok" : 1